FIG. 16 is a schematic view showing a plating apparatus which is an example of a substrate electrolytic processing apparatus. As shown in FIG. 16, the plating apparatus includes a plating bath 101 for holding a plating solution therein, an anode 102 disposed in the plating bath 101, an anode holder 103 holding the anode 102, and a substrate holder 104. The substrate holder 104 is configured to detachably hold a substrate W, such as a wafer, and immerse the substrate W in the plating solution held in the plating bath 101. The anode 102 and the substrate W are disposed in a vertical position and opposite each other in the plating solution.
The plating apparatus further includes a paddle 105 for agitating the plating solution in the plating bath 101, and a regulation plate 106 for regulating a distribution of electric potential on the substrate W. The regulation plate 106 is disposed between the paddle 105 and the anode 102, and has an opening 106a for restricting an electric field, in the plating solution. The paddle 105 is located near a surface of the substrate W held by the substrate holder 104. The paddle 105 is disposed in a vertical position, and is configured to reciprocate parallel to the surface of the substrate W to thereby agitate the plating solution so that a sufficient amount of metal ions can be supplied uniformly to the surface of the substrate W during plating of the substrate W.
The anode 102 is coupled to a positive electrode of a power source 107 through the anode holder 103, and the substrate W is coupled to a negative electrode of the power source 107 through the substrate holder 104. When a voltage is applied between the anode 102 and the substrate W, an electric current is passed to the substrate W, so that a metal film is formed on the surface of the substrate W.
FIG. 17 is a view from arrow A shown in FIG. 16. In FIG. 17, the substrate holder 104 is not depicted. In FIG. 17, the substrate W has a diameter of 300 mm. A width of the paddle 105 is smaller than the diameter of the substrate W. The paddle 105 includes a plurality of agitation rods 108 extending in a vertical direction. The agitation rods 108 are arranged at equal intervals. Since the paddle 105 is located in the electric field between the anode 102 and the substrate W, the agitation rods 108 reciprocates from side to side as shown by arrows while shielding the substrate from the electric field.
FIG. 18 is a graph showing electric-field shielding rate. The electric-field shielding rate is a ratio of a time during which the paddle 105 shields the substrate from the electric field to a total time of the reciprocation of the paddle 105. A horizontal axis in FIG. 18 represents distance [mm] from a center of the substrate W and a vertical axis represents the electric-field shielding rate. A thick line shown in FIG. 18 represents mean value of the electric-field shielding rate. It can be seen from FIG. 18 that the electric-field shielding rate sharply drops in a region in which the distance from the center of the substrate W exceeds 100 mm. When the electric-field shielding rate decreases, an electric current density on the substrate W increases, and the metal film, formed on the substrate W, becomes thick. As shown in FIG. 18, the electric-field shielding rate at a peripheral portion of the substrate W is lower than the electric-field shielding rate at a central portion of the substrate W. Accordingly, the metal film at the peripheral portion of the substrate W is thicker than the metal film at the central portion of the substrate W. As a result, the thickness of the metal film formed on the substrate W becomes non-uniform.
If the width of the paddle 105 is made larger than the diameter of the substrate W, it is possible that the electric-field shielding rate is uniform. However, the plating bath 101 that houses the paddle 105 must be large, resulting in an increase in size of the entirety of the plating apparatus.